The complex formation of nitrate ions with nickel(II) in dry [C4mim][Tf2N] ionic liquid (IL) was investigated by means of UV-visible spectrophotometry, isothermal titration calorimetry (ITC), extended X-ray absorption fine structure spectroscopy (EXAFS), and molecular dynamics (MD) simulations. EXAFS spectroscopy and MD simulations show that the solvated Ni(II) cation is initially coordinated by the oxygens of the [Tf2N](-) anion of IL, which can behave either as mono- or bidentate. Spectroscopic and thermodynamic data show that Ni(II) is able to form up to three stable mononuclear complexes with nitrate in this solvent. The stability constants for Ni(NO3)j complexes (j = 1-3) calculated from spectrophotometry and ITC experiments decrease in the order log K1 > log K2 > log K3. The formation of the first two species is enthalpy-driven, while the third species is entropy-stabilized. The UV-vis spectra of solutions containing different nitrate/Ni(II) ratios show that the metal ion retains the six-coordinate geometry. Furthermore, the EXAFS evidences that nitrate is always bidentate. Molecular dynamics simulations show that the [Tf2N](-) anions bind Ni(II) through the sulfonyl oxygen atoms and can coordinate either as monodentate or chelate. The analysis of the MD data shows that introduction of nitrates in the first coordination sphere of the metal ion results in remarkable structural rearrangement of the ionic liquid.

Mesoporous Hierarchical Alumina Microspheres (HAM) with high efficiency for fluoride removal have been synthesized and characterized. Two types of HAM, differing mostly in crystallinity, surface area and pore size have been obtained. Fluoride adsorption studies have been carried out by means of potentiometry and Isothermal Titration Calorimetry (ITC). The latter method has been applied for the first time to obtain direct determination of the adsorption enthalpy (DHads)ofF? ion on HAM. The kinetics of the reaction revealed a two-step process for fluoride adsorption on the adsorbent material. The DHads values obtained are clearly negative for the different samples investigated. Experimental adsorption data are well fitted by a Langmuir isotherm. The adsorption constant obtained for type A is 1 order of magnitude higher than for type B, showing that the synthetic protocol has a remarkable effect on this parameter. The highest defluoridation capacity reaches 26 mmol g?1 after 1 hour of equilibration for the amorphous HAM, which is higher than for other adsorbents reported in the literature

β-Cyclodextrin (β-CD) is a nontoxic cyclic oligosachcharide that can encapsulate all or part of organic molecules of appropriate size and specific shape through noncovalent interaction. Herein, we report the influence of β-CD complex formation of an antipyrine derivative on its metal ion sensing behavior. In aqueous solution, the antipyrine shows a turn-on fluorescence sensing of vanadyl ion, and in cyclodextrin medium it senses aluminum ion. The compound shows an unusual fluorescence quenching on binding with β-cyclodextrin (log K SV = 2.34 ± 0.02). The differential metal ion sensing is due to the partial blocking of the chelating moiety by the cyclodextrin molecule. The structure of the antipyrine− cyclodextrin complex is optimized by two-dimensional rotating-frame Overhauser effect spectroscopy. The binding constant is determined by isothermal titration calorimetry (log K = 2.09 ± 0.004). The metal ion binding site is optimized by quanutm mechanical calculations. The lower limit of detection of vanadyl and aluminum ions, respectively, are 5 × 10 −8 and 5 × 10 −7 mol dm −3 . This is the first report of selectivity of two different cations by a chemosensor in water and in β-CD.

Superparamagnetic iron nanoparticles (SPION) have been functionalized with 3mercaptopropionic acid (3-MPA), characterized and applied for the removal of Ag + , Hg 2+ and Pb 2+ metal ions from aqueous solutions by iron oxide (Fe3O4). The heavy metal adsorption has been investigated by means of ICP-OES and isothermal titration calorimetry. Experimental data ware better fitted by Langmuir rather than Freundlich isotherms and the thermodynamic parameters for the adsorption process of the metal ions on the functionalized SPION nanoparticles (SPION@3-MPA) were obtained. Isothermal titration calorimetry (ITC) is applied to monitor heavy metal adsorption on SPION@3-MPA: the process results to be exothermic for Hg 2+ , Ag + while it is weakly endothermic in the case of Pb 2+ and the adsorption enthalpies and entropies have been obtained. The values of the thermodynamic parameters suggest that the Ag + and Hg 2+ ions interact strongly with the thiol groups, while the Pb 2+ ions seem to be adsorbed by the material mostly via electrostatic interaction. When compared to other thiol-functionalized materials, the obtained SPION@3-MPA NP can be considered a competitive adsorbent for Ag + and Hg 2+ ions. The comparison between the ICP-OES adsorption rata and the enthalpy trend obtained by ITC supports shows that the latter technique can be a good tool for a fast testing of materials to be applied for heavy metal separation from solutions.